NaturalSelectionProtocol
Evolution by Natural Selection Revision
Question 1: Describe what is happening in figures 1-3. Is the
population of mice different in figure 3 than in figure 1? Explain
why.
Living things that are well adapted to their environment survive
and reproduce. Those that are not well adapted don’t survive and
reproduce. An adaptation is any characteristic that increases
fitness, which is defined as the ability to survive and
reproduce.
Question 2: For the mice in the figure, what characteristic was
an adaptation that increased fitness?
Question 3: The table describes four female mice that live in a
beach area which is mostly tan sand with scattered plants.
Characteristics
of each female mouse
Color of Fur
Black
Tan
Tan and Black
Cream
Running speed
8 cm/sec.
6 cm/sec.
7 cm/sec.
5 cm/sec.
# pups produced by each female
0
11
5
4
Age at death
2 months
8 months
4 months
4 months
Question 4: According to the definition given above for fitness,
which mouse would biologists consider the fittest? Explain why this
mouse would be the fittest.
Question 5: If a mouse's fur color is generally similar to its
mother’s color, which color fur would be the most common among the
pup
1
REVISION OF HERITABLE TRAITS AND NATURAL SELECTION
A characteristic, which is influenced by genes and passed from
parents to offspring, is called heritable. For the mice on the tan
sand, fur color was a heritable characteristic. As you saw, tan fur
was a heritable adaptive characteristic, which became more common
in the pups.
In general, individuals with heritable adaptive characteristics
survive longer and have more offspring, which have similar adaptive
characteristics. Therefore, a heritable adaptive characteristic
will tend to become more common in the population. This process is
called evolution by natural selection.
Evolution by natural selection leads to adaptation within a
population. The term evolution by natural selection does not refer
to individuals changing, only to changes in the frequency of
adaptive characteristics in the population as a whole. For example,
for the mice that lived on tan sand, none of the mice had a change
in the color of their fur; rather, due to natural selection, tan
fur was more common for the pups than for the mother mice.
Question 6: Explain why a heritable characteristic which helps
an animal to live longer will generally tend to become more common
in subsequent generations as a result of evolution by natural
selection.
Question 7: Suppose an unusual heritable characteristic helped
animals to live longer but made them sterile so they could not have
any offspring. Explain why this heritable characteristic would not
become more common in subsequent generations as a result of
evolution by natural selection.
The following example illustrates a more complete definition of
fitness as the ability to survive and produce offspring who can
also survive and reproduce. According to this definition of him
fitness, which of the four male lions described below would
biologists consider the “fittest”?
Name
George
Dwayne
Spot
Tyrone
Age at death
13 years
16 years
12 years
10 years
# cubs fathered
19
25
22
22
# cubs surviving to adulthood
15
14
14
19
Size
10 feet
8.5 feet
9 feet
9 feet
Question 8: Explain why Dwayne was not the fittest even though
he lived the longest and fathered the most cubs.
Question 9: Complete the following table.
If the reason why more of
Tyrone's cubs survived was:
Would the offspring of Tyrone's cubs inherit characteristics
that
increased their chances of surviving to adulthood? Explain why
or why not.
Tyrone had heritable
characteristics that increased resistance to infections, and
many of his cubs inherited these characteristics.
Tyrone happened to live near
a farmer whose children liked watching lion cubs, so for ten
years the farmer put out meat with antibiotics for Tyrone's
cubs.
Use this example to explain why natural selection does not
operate on a characteristic which affects fitness but is not
heritable.
Question 10:
This series of pictures shows natural selection in a population
of cacti. Pictures 1 and 2 show what happened when a deer came to
eat, picture 3 shows the cacti a few weeks later (notice the
flowers on the right-hand cactus), and picture 4 shows the
situation a few months later.
12
34
Complete the following table to describe how this cactus example
illustrates the three necessary conditions for evolution by natural
selection.
Necessary Condition for
Evolution by Natural Selection
How does the cactus example
illustrate this condition?
Question 11: "Survival of the fittest" is a common expression.
What do you think most people mean by this expression?
Question 12: How would you explain this expression to help
someone understand how natural selection actually functions?
